Thus far, a copper alloy sheet having high conduction and high strength has been used for a constituent material of connectors, terminals, relays, springs, switches and the like that have been used in electric components, electronic components, vehicle components, communication devices, electronic and electric devices and the like. However, the recent decreases in the size and weight of the devices and the recent performance enhancement require extremely advanced improvement in the characteristics of constituent materials used in the devices. For example, an extremely thin sheet is used in a spring contact point of a connector, and a high-strength copper alloy that constitutes the extremely thin sheet needs to have high strength or highly balanced elongation and strength in order to decrease the thickness of the sheet. Furthermore, the high-strength copper alloy also needs to have excellent productivity and economic efficiency and to prevent the occurrence of problems in terms of conduction, corrosion resistance (stress corrosion cracking resistance, dezincification corrosion resistance and migration resistance), stress relaxation characteristics, solderability and the like.
In addition, in constituent materials of connectors, terminals, relays, springs, switches and the like that are used in electric components, electronic components, vehicle components, communication devices, electronic and electric devices and the like, there are components and portions which require higher strength or a higher conductivity in order to decrease the thickness with preconditions of excellent elongation and excellent bending workability. However, strength and conductivity are contradictory characteristics, and thus, when strength improves, it is general for conductivity to decrease. Among the above, there are components that are a high-strength material and need to have a higher conductivity (21% IACS or more, for example, approximately 25% IACS) at a tensile strength of 580 N/mm2 or more. In addition, there are components that need to have superior stress relaxation characteristics and superior thermal resistance in a place with a high operation environment temperature such as a place near an engine room in an automobile.
Furthermore, in addition to connectors, terminals, relays and the like, there are component constituent materials of sliding pieces, bushes, bearings and liners which need to have high strength, favorable elongation, balanced strength and elongation, and excellent corrosion resistance, particularly, a variety of clasps that need to have strength, workability and corrosion resistance such as sliding liners in automatic pile drivers, clothing clasps and spring cooler clasps, and a variety of devices for which there are tendencies of size decrease, weight decrease, reliability improvement and performance enhancement such as filters in a variety of strainers.
Generally, beryllium copper, phosphor bronze, nickel silver, brass and Sn-added brass are well known as high strength and high conduction copper alloys, but the ordinary high-strength copper alloys have the following problems, and thus cannot satisfy the above requirements.
Beryllium copper has a highest strength among copper alloys, but beryllium is extremely harmful to human bodies (particularly, in a molten state, even an extremely small amount of beryllium vapor is very dangerous). In addition, the disposal treatment (particularly, incineration treatment) of beryllium copper members or products including beryllium copper members is difficult, and the initial cost necessary for a melting facility used to manufacture beryllium copper becomes extremely high. Therefore, not only is a solution treatment required in the final stage of manufacturing in order to obtain desired characteristics, but there is also a problem with economic efficiency including manufacturing costs.
Since phosphor bronze and nickel silver have poor hot workability and are not easily manufactured through hot rolling, generally, phosphor bronze and nickel silver are manufactured through horizontal continuous casting. Therefore, the productivity is poor, the energy cost is high, and the yield is also poor. In addition, since large amounts of expensive Sn and expensive Ni are contained in phosphor bronze for springs or nickel silver for springs which are representative high-strength products, there is a problem with economic efficiency, and both have poor conductivity.
While brass and Sn-added brass are cheap, they do not have satisfactorily balanced strength and elongation, have poor stress relaxation characteristics, and have a problem with corrosion resistance (stress corrosion and dezincification corrosion resistance), and therefore brass and Sn-added brass are inappropriate as constituent materials for products that need to achieve size decrease, reliability improvement and performance enhancement.
Therefore, the ordinary high conduction and high-strength copper alloys are unsatisfactory as a component constituent material for a variety of devices for which there are tendencies of size decrease, weight decrease, reliability improvement and performance enhancement as described above, and there is a strong demand for development of new high conduction and high-strength copper alloys.
As an alloy for satisfying the above requirements of high conduction, high strength and the like, for example, a Cu—Zn—Sn alloy described in Patent Document 1 is known. However, the alloy according to Patent Document 1 is still insufficient in terms of strength and the like.